Resin sheet, liquid crystal cell substrate comprising the same

ABSTRACT

A resin sheet that is unlikely to be affected by heat and allows prevention of the occurrence of a crack is provided. A glass fiber cloth-like material is dipped into an epoxy resin solution and subjected to curing, thereby obtaining an epoxy resin-based sheet including the glass fiber cloth-like material. The resin sheet has a haze value of 10% or lower, and preferably, has a light transmittance of 88% or higher, an in-plane retardation of not more than 2 nm, a retardation in a thickness direction of 40 nm, and a surface roughness of not more than 2 μm.

This application is a 371 of PCT/JP03/06372, filed May 22, 2003.

TECHNICAL FIELD

The present invention relates to a resin sheet, specifically, a resinsheet that is useful for a liquid crystal cell substrate, and a liquidcrystal cell substrate using the same.

BACKGROUND ART

Conventionally, in liquid crystal displays, as a liquid crystal cellsubstrate for supporting a liquid crystal to form a liquid crystal cell,glass-based substrates have been used from the viewpoints of theirstrength and heat resistance. However, in recent years, the upsizing ofliquid crystal displays has created a demand for, for example, areduction in the weight and thickness of the liquid crystal cellsubstrate. With respect to this demand, as an alternative material tothe glass-based substrates, a resin sheet formed from an epoxy resin orthe like has been proposed and commercialized (for example, see JP6(1994)-337408 A, JP 7(1995)-199165 A). Further, for EL displays and thelike, with the same background as above, the application of a resinsheet as described above also has been proposed.

However, in such a resin sheet formed from an epoxy resin or the like,shrinkage and expansion due to the influence of thermal expansion andmoisture may be caused. This has led to the problem of positionaldeviation caused, for example, when forming an electrode and whenforming a color filter. In order to avoid this problem, an attempt hasbeen made in which spherical inorganic oxide particles having a meanparticle diameter of about 1 nm to 100 μm are dispersed in the resinsheet so that the coefficient of linear expansion is suppressed to notmore than 5.00×10⁻⁵/° C. (for example, see JP2002-351353 A). However,the above-described resin sheet in which the spherical inorganic oxideparticles are dispersed is decreased in strength. Therefore, forexample, during transport or when forming a liquid crystal panel,cracking or the like is caused, which has been problematic in terms ofproduction efficiency.

DISCLOSURE OF THE INVENTION

In order to solve the above-mentioned problems, it is an object of thepresent invention to provide a resin sheet that is unaffected by heatand has excellent strength and transparency. More specifically, thisinvention provides a resin sheet that is useful for a substrate forvarious types of displays such as a liquid crystal display and the likeand a solar cell and the like.

In order to achieve the above-described object, the resin sheetaccording to the present invention is characterized by including anepoxy resin and a glass fiber cloth-like material and having a hazevalue of 10% or lower.

By including the glass fiber cloth-like material as described above, theresin sheet according to the present invention not only can achieve alow coefficient of linear expansion but also combines excellent strengthand flexibility (bending properties). As described above, the resinsheet has a low coefficient of linear expansion, and thus, for example,when the resin sheet is used as a liquid crystal cell substrate informing a liquid crystal panel, the above-described thermal expansioncan be suppressed, and positional deviation of an electrode and a colorfilter that is attributable to the thermal expansion also can beavoided. Further, the resin sheet has excellent strength andflexibility, and thus, for example, cracking of the resin sheet due tovibrations caused during transport also can be prevented. Moreover, theresin sheet according to the present invention has a haze value of 10%or lower and thus has excellent transparency. Therefore, for example,when used as a liquid crystal cell substrate, an EL device substrate orthe like in assembling various types of image displays, the resin sheetallows characters and images to be displayed with higher definition andthus is useful in achieving an extremely high displaying quality.Further, having a haze value of 10% or lower, the resin sheet accordingto the present invention is particularly useful as, for example, atransmission-type liquid crystal cell substrate.

In the present invention, the haze value can be measured based on, forexample, JIS K 7136. Specifically, the measurement can be performedusing a commercially available hazemeter (for example, HM-150, a tradename, manufactured by Murakami Color Research Laboratory). Thismeasuring method is used only to determine the haze value of theabove-described resin sheet and not to limit the present invention interms of the method of manufacturing the resin sheet, the use of theresin sheet and the like.

The resin sheet according to the present invention attains theabove-described effects and thus is useful as various types ofsubstrates such as a liquid crystal cell substrate, anelectroluminescent (EL) substrate, a substrate for a solar cell and thelike.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing an example of a resin sheetaccording to the present invention.

FIG. 2 is cross-sectional view showing another example of the resinsheet according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

As described above, the resin sheet according to the present inventionis characterized by including an epoxy resin and a glass fibercloth-like material and having a haze value of 10% or lower.

In the present invention, as the “glass fiber cloth-like material”, forexample, a woven fabric, a nonwoven fabric, and a knitted fabric can beused. Specifically, for example, conventionally known products availableon the market such as a glass cloth woven from yarn, a glass nonwovenfabric, a roving cloth, a chopped strand mat, a unidirectional wovenroving (cord fabric) and the like can be used.

The glass fiber cloth-like material has, for example, a density (weight)in a range of, preferably 10 to 500 g/m², more preferably 20 to 350g/m², and most preferably 30 to 250 g/m². Further, the glass fiber has afilament thickness of, for example, 3 to 15 μm, preferably 5 to 13 μm,and most preferably 5 to 10 μm.

The glass fiber cloth-like material has a thickness of, for example, 10to 500 μm, preferably 15 to 350 μm, and most preferably 30 to 250 μm.

There is no particular limit to the embodiment of the resin sheetaccording to the present invention as long as the epoxy resin and theglass fiber cloth-like material are included therein. For example,preferably, the resin sheet includes the glass fiber cloth-like materialand a resin layer containing the epoxy resin, and is a single-layeredbody into which the resin layer and the glass fiber cloth-like materialare integrated. Specifically, for example, preferably, the resin layeris formed of the epoxy resin that is cured in the state of beingimpregnated into the glass fiber cloth-like material. In a morepreferable embodiment of the resin sheet, the glass fiber cloth-likematerial is embedded in the resin layer containing the epoxy resin. Inthe present invention, the epoxy resin layer refers to a layer made upof a cured body containing an epoxy resin, and may contain as well asthe epoxy resin, for example, various additives such as, for example, acuring agent that will be described later.

The cross-sectional view of FIG. 1 shows an example of a preferredembodiment of the resin sheet according to the present invention. Thisresin sheet 10 is a single-layered body into which an epoxy resin and aglass fiber cloth-like material are integrated. A glass fiber cloth-likematerial 2 is embedded inside an epoxy resin layer 1. The epoxy resin isimpregnated inside the glass fiber cloth-like material 2 and cured, sothat the epoxy resin and the glass fiber cloth-like material 2 areintegrated. In the figure, “dots” are used to show the epoxy resin.

There is no particular limit to the epoxy resin, and conventionallyknown types of epoxy resins can be used. Examples of such epoxy resinsinclude: bisphenol resins such as a bisphenol A type, a bisphenol Ftype, a bisphenol S type, and hydrogenated derivatives thereof and thelike; novolak resins such as a phenol novolak type, a cresol novolaktype and the like; nitrogen-containing cyclic resins such as atriglycidylisocyanurate type, a hydantoin type and the like; aromaticresins such as an alicyclic type, an aliphatic type, a naphthalene typeand the like; low-water absorptive resins such as a glycidyl ether type,a biphenyl type and the like; dicyclo resins such as a dicyclopentadienetype and the like; ester resins; ether ester resins; and modificationsthereof. Among the above-mentioned types of epoxy resins, the bisphenolA type epoxy resin, the alicyclic epoxy resin, thetriglycidylisocyanurate type epoxy resin, and the dicyclopentadiene typeepoxy resin are used preferably from the viewpoints of prevention ofdiscoloration and the like. These types of epoxy resins may be usedalone or in the form of a combination of two or more types. Thebisphenol A type epoxy resin is expressed by, for example, the followingformula (1), in which n denotes, for example, 0 to 2.

These types of epoxy resins may be used alone or in the form of acombination of two or more types. Particularly, it is preferable to usethe dicyclopentadiene type epoxy resin and the alicyclic epoxy resin incombination because this combination provides heat resistance andtoughness in excellent balance.

Specific examples of the alicyclic epoxy resin include3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate that isexpressed by the following formula (2), and a compound expressed by thefollowing formula (3). In the following formula (3), n denotes aninteger of 1 to 20, and R denotes an alkyl group.

Furthermore, as the epoxy resin, an epoxy resin having adicyclopentadiene skeleton, specifically, for example, epoxy resins thatare expressed by the following formulae (4) and (5) can be used. In thefollowing formula (5), n denotes 1 to 3.

Among these types of epoxy resins, the epoxy resin expressed by theabove-mentioned formula (4) or (5) is used most preferably for thefollowing reason. That is, by the use of these resins, particularly, theresin sheet can be controlled so as to have a small retardation value inthe thickness direction. In the case where a retardation in thethickness direction is small as described above, as will be describedlater, for example, when the resin sheet according to the presentinvention is used in a liquid crystal display, light leakage from adiagonal direction during a black display can be suppressedsufficiently, and thus the display properties further are enhanced.

For example, in order to form a resin sheet having increasedflexibility, strength and the like, the epoxy resin has, preferably anepoxy equivalent of 100 to 1,000 (g/eq) and a softening point of 120° C.or lower, and more preferably an epoxy equivalent of 150 to 500 (g/eq)and a softening point of 80° C. or lower. Further, it is preferable thatthe epoxy resin is in liquid form at an atmospheric temperature (forexample, 5 to 35° C.).

Furthermore, when forming the resin sheet according to the presentinvention as will be described later, a two-pack mixing type epoxyresin, which is in a liquid state at a temperature not higher than atemperature at which coating is performed, particularly, at anatmospheric temperature, exhibits excellent expandability and coatingproperties and thus is used preferably.

In the resin sheet according to the present invention, the resin layercontaining the epoxy resin constitutes, for example, 20 to 80 wt %,preferably 25 to 75 wt %, and more preferably 30 to 70 wt %. Further, inthe resin layer, the epoxy resin constitutes, for example, 30 to 100 wt%, preferably 40 to 90 wt %, and more preferably 40 to 80 wt %.Meanwhile, in the resin sheet, the glass fiber cloth-like material isincluded at a ratio of, for example, 20 to 80 wt %, preferably 25 to 75wt %, and more preferably 30 to 70 wt %.

The epoxy resin layer may contain, for example, various additives asrequired, examples of which include conventionally known additives suchas a curing agent, a curing accelerator, an antioxidant, a denaturant, asurfactant, a dye, a pigment, a discoloration inhibitor, an ultravioletabsorber and the like. For example, any one of these additives may beadded, or these additives may be used in the form of a combination oftwo or more types.

There is no particular limit to the curing agent. Examples of the curingagent include organic acid compounds such as tetrahydrophthalic acid,methyltetrahydrophthalic acid, hexahydrophthalic acid,methylhexahydrophthalic acid and the like, and amine compounds such asethylenediamine, propylenediamine, diethylenetriamine,triethylenetetramine, amine adducts thereof, methaphenylenediamine,diaminodiphenylmethane, and diaminodiphenylsulfone and the like. Forexample, any one of these curing agents may be used, or these curingagents may be used in the form of a combination of two or more types.

Furthermore, in addition to the above-mentioned curing agents, furtherexamples of the curing agent include amide compounds such asdicyandiamide, polyamide and the like, hydrazide compounds such asdihydrazide and the like, imidazole compounds such as methylimidazole,2-ethyl-4-methylimidazole, ethylimidazole, isopropylimidazole,2,4-dimethylimidazole, phenylimidazole, undecylimidazole,heptadecylimidazole, 2-phenyl-4-methylimidazole and the like,imidazoline compounds such as methylimidazoline,2-ethyl-4-methylimidazoline, ethylimidazoline, isopropylimidazoline,2,4-dimethyl-imidazoline, phenylimidazoline, undecylimidazoline,heptadecylimidazoline, 2-phenyl-4-methylimidazoline and the like, phenolcompounds, urea compounds, and polysulfide compounds.

Moreover, acid anhydrides and the like also can be used as the curingagent and are preferable from the viewpoints of, for example, preventionof discoloration and the like. Specific examples of an acid anhydrideinclude phthalic anhydride, maleic anhydride, trimellitic anhydride,pyromellitic anhydride, nadic anhydride, glutaric anhydride,tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride,hexahydrophthalic anhydride, methylhexahydrophthalic anhydride,methylnadic anhydride, dodecenylsuccinic anhydride, dichlorosuccinicanhydride, benzophenonetetracarboxylic anhydride, and chlorendicanhydride. Of these acid anhydrides, particularly, colorless or paleyellow acid anhydrides having a molecular weight of about 140 to about200 are used preferably. Examples of such acid anhydrides includephthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalicanhydride, methylhexahydrophthalic anhydride, and methylnadic anhydride.

There is no particular limit to the proportion in which the epoxy resinand the curing agent are mixed. In the case of using an acidanhydride-based curing agent as the curing agent, for example, an acidanhydride is mixed so as to attain, preferably 0.5 to 1.5 equivalents,and more preferably 0.7 to 1.2 equivalents, per equivalent of an epoxygroup in an epoxy resin. With the acid anhydride mixed in an amount ofnot less than 0.5 equivalents, a further improvement in color tint isobtained after curing, and with the acid anhydride mixed in an amount ofnot more than 1.5 equivalents, sufficient moisture resistance can bemaintained. In the cases of using other curing agents and in the case ofusing one or more types of curing agents in combination, mixing also canbe performed according to, for example, the above-mentioned proportions.

There is no particular limit to the curing accelerator, and, forexample, tertiary amines, imidazoles, quaternary ammonium salts,quaternary phosphonium salts, organic metal salts, phosphorus compounds,and urea compounds and the like can be used. Among these compounds,particularly, tertiary amines, imidazoles, and quaternary phosphoniumsalts are used preferably. For example, these curing accelerators may beused alone or in the form of a combination of two or more types.

There is no particular limit to the proportion in which the curingaccelerator is mixed, and the proportion can be determined appropriatelyaccording to, for example, the amount and type of an epoxy resin.Specifically, for example, a curing accelerator is in an amount,preferably of 0.05 to 7.0 parts by weight, and more preferably in arange of 0.2 to 3.0 parts by weight, per 100 parts by weight of an epoxyresin. With the curing accelerator mixed in an amount of not less than0.05 parts by weight, an effect of accelerating curing can be attainedsufficiently, and with the curing accelerator mixed in an amount of notmore than 7.0 parts by weight, a further improvement in color tint isobtained after curing.

There is no particular limit to the antioxidant, and, for example,conventionally known compounds such as phenols, amines, organosulfurcompounds, phosphines and the like can be used.

There is no particular limit to the denaturant, and, for example,conventionally known compounds such as glycols, silicones, alcohols andthe like can be used.

There is no particular limit to the addition of the surfactant. Forexample, when forming an epoxy resin sheet by allowing an epoxy resin tobe cured while being in contact with air, the surfactant can be added sothat the sheet has a smooth surface. As the surfactant, for example,various surfactants such as silicone, acrylic, and fluorinatedsurfactants and the like can be used, and among these surfactants, thesilicone surfactants are used preferably.

The resin sheet according to the present invention may be asingle-layered body including the epoxy resin and the glass fibercloth-like material, namely, a single epoxy resin layer with the glassfiber cloth-like material included therein, or a laminated body inwhich, in addition to the single-layered body, other sheets that will bedescribed later are laminated.

In the resin sheet according to the present invention, an absolute valueof a difference between a refractive index of the glass fiber cloth-likematerial and a refractive index of the resin layer containing the epoxyresin is, preferably 0 to 0.01, more preferably 0 to 0.008, and mostpreferably 0 to 0.006 for the following reason. That is, with theabsolute value being not more than 0.01, interface scattering causedbetween the glass fiber cloth-like material and the resin layer can besuppressed sufficiently, and the haze value of the resin sheet can bedecreased, thereby allowing sufficient transparency to be maintained. Inthe present invention, the refractive indexes can be determined by, forexample, measurement using an Abbe refractometer performed under acondition of a temperature of 25° C. and light with a wavelength of 589nm. In this relationship between the respective refractive indexes, theresin layer containing the epoxy resin refers to, for example, a curedbody constituting a portion of the resin sheet except for the glassfiber cloth-like material.

It is preferable that the resin sheet according to the present inventionhas a coefficient of linear expansion of not more than 3.00×10⁻⁵/° C. ata temperature of 25° C. to 160° C. for the following reason. That is,with a coefficient of linear expansion not more than the above-mentionedvalue, in the case where the resin sheet according to the presentinvention is used as a liquid crystal cell substrate, and a color filterand an electrode are formed on the surface thereof, positional deviationand the like attributable to thermal expansion can be suppressedsufficiently, and thus the process of forming the color filter or thelike further is facilitated. Further, the coefficient of linearexpansion is, more preferably not more than 2.00×10⁻⁵/° C., and mostpreferably 0 to 1.5×10⁻⁵/° C.

The coefficient of linear expansion can be determined, for example, inthe following manner. That is, with respect to a sample, a TMA measuredvalue is obtained by the TMA method specified in JIS K-7197 and issubstituted into the following expression. In the following expression,ΔIs(T₁) and ΔIs(T₂) indicate TMA measured values (μm) obtainedrespectively at a temperature T₁ (° C.) and a temperature T₂ (° C.), atwhich the measurement was performed with respect to the sample, and L₀indicates a length (mm) of the sample at a room temperature of 23° C.

Coefficient of linear expansion=[1/(L₀×10³)]·[(ΔIs(T₂)−ΔIs(T₁))/(T₂−T₁)]

The resin sheet according to the present invention has a haze value of,suitably 10% or lower as described above, more preferably 3% or lower,and most preferably 0 to 2%.

It is preferable that the resin sheet according to the present inventionhas a light transmittance of 88% or higher for the following reason.That is, with a light transmittance not lower than the above-mentionedvalue, for example, when the resin sheet is used as a liquid crystalcell substrate, an EL device substrate or the like in assembling varioustypes of image displays, characters and images can be displayed withhigher definition, thereby achieving a higher displaying quality.Further, the light transmittance is, more preferably 90% or higher, andmost preferably 92 to 100%. The light transmittance can be determinedby, for example, measuring a total transmittance of light rays with awavelength of 550 nm using a high-speed spectrophotometer.

It is preferable that the resin sheet according to the present inventionhas an in-plane retardation of not more than 2 nm for the followingreason. That is, with an in-plane retardation not more than theabove-mentioned value, when the resin sheet is used as a liquid crystalcell substrate, an EL device substrate or the like, the contrast,particularly, the contrast in an oblique direction of an image displayis improved further, and thus an excellent displaying quality isexhibited. Further, the in-plane retardation is, more preferably 0 to 1nm, and most preferably 0 to 0.8 nm.

Furthermore, preferably, the resin sheet according to the presentinvention has a retardation in the thickness direction of not more than40 nm for the following reason. That is, with a retardation in thethickness direction of not more than the above-mentioned value, when theresin sheet is used in an image display as described above, lightleakage from an oblique direction can be suppressed sufficiently, andthe contrast in the oblique direction is improved further, and thus anexcellent displaying quality is exhibited. The retardation in thethickness direction is, more preferably not more than 20 nm, even morepreferably 0 to 10 nm, and still more preferably 0 to 7 nm. In the casewhere the retardation in the thickness direction is set to a value notmore than 40 nm, particularly, not more than 20 nm, it is mostpreferable to use the epoxy resin expressed by the above-mentionedformula (4) or (5).

The above-mentioned in-plane retardation (Δnd) and the retardation inthe thickness direction (Rth) are expressed respectively by, forexample, the following expressions. In the following expressions, nx,ny, and nz indicate the respective refractive indexes in directions ofan X axis, a Y axis, and a Z axis in the resin sheet. The X axisdirection refers to an axis direction in which the resin sheet has themaximum refractive index in the plane thereof. The Y axis directionrefers to an axis direction perpendicular to the X axis in the plane.The Z axis direction refers to a thickness direction perpendicular tothe X axis and the Y axis. Further, d indicates the thickness of theresin sheet.Δnd=(nx−ny)·dRth=[{(nx+ny)/2}−nz]·d

Preferably, in the resin sheet according to the present invention, atleast one surface of the resin sheet is smooth for the following reason.That is, by forming the surface so that it is smooth as described above,for example, when the resin sheet is used as a liquid crystal cellsubstrate, the process of forming an alignment film, a transparentelectrode or the like on the surface further is facilitated.Specifically, preferably, the at least one surface has a surfaceroughness (Rt) of, for example, not more than 2 μm. In the presentinvention, a “surface roughness” refers to a difference between amaximum value and a minimum value that are obtained by measurement usinga stylus type surface roughness meter (for example, P-11, trade name;manufactured by KLA-Tencor Japan Ltd.) under a condition of a longwavelength cut-off of 800 μm, a short wavelength cut-off of 250 μm, andan evaluation length of 10 mm.

In the case where the resin sheet according to the present invention isthe single-layered body, there is no particular limit to the thicknessof the resin sheet. Preferably, in this case, the resin sheet has athickness in a range of, for example, 20 to 800 μm for the followingreason. That is, with the thickness being not less than 20 μm,sufficient strength and rigidity can be maintained. Further, with thethickness being not more than 800 μm, for example, a thickness andweight reduction can be realized sufficiently. The thickness is, morepreferably 30 to 500 μm, and most preferably 50 to 300 μm.

The resin sheet according to the present invention may be a laminatedbody further including, in addition to the single-layered body describedabove, at least one of a hard-coat layer and a gas barrier layer.Preferably, the resin sheet is a laminated body including both of thehard-coat layer and the gas barrier layer. Particularly, with thehard-coat layer laminated as an outermost layer, for example, theabrasion resistance and the like of the sheet can be increased. Further,in each of various types of image displays such as a liquid crystaldisplay and the like, when moisture and oxygen are transmitted through aliquid crystal cell substrate to enter a liquid crystal cell, thequality of a liquid crystal changes and bubbles are formed, which maycause deterioration in appearance, disconnection of a conductive filmpattern, and the like. However, by providing the gas barrier layer, forexample, the transmission of moisture, oxygen and the like through gascan be prevented. Further, each of the hard-coat layer and the gasbarrier layer may be laminated on either one or each of surfaces.

In the case of including both of the hard-coat layer and the gas barrierlayer, there is no particular limit to the order of layer lamination.Preferably, in this case, the order of layer lamination is the epoxyresin layer, the gas barrier layer, and the hard-coat layer.Particularly, the hard-coat layer has excellent impact resistance,chemical resistance and the like and thus preferably is laminated as anoutermost layer. Further, another hard-coat layer may be laminated alsoon the other surface of the epoxy resin layer. The cross-sectional viewof FIG. 2 shows an example of the resin sheet according to the presentinvention, which includes a hard-coat layer and a gas barrier layer asdescribed above. In the figure, like portions are identified by the samereference numerals as in FIG. 1. As shown in the figure, in this resinsheet 20, a gas barrier layer 3 is laminated on one surface of an epoxyresin layer 1 containing a glass fiber cloth-like material 2, and ahard-coat layer 4 is laminated further on the gas barrier layer 3.

There is no particular limit to a material for forming the hard-coatlayer. Examples of the material include urethane resins, acrylic resins,polyester resins, polyvinyl alcohol resins such as polyvinyl alcohol, anethylene vinyl alcohol copolymer and the like, vinyl chloride resins,and vinylidene chloride resins. Further, for example, polyarylateresins, sulfone resins, amide resins, imide resins, polyether sulfoneresins, polyether imide resins, polycarbonate resins, silicone resins,fluororesins, polyolefin resins, styrene resins, vinylpyrrolidoneresins, cellulose resins, acrylonitrile resins and the like also can beused. Among these materials, urethane resins are used preferably, andmore preferably, urethane acrylate is used. These types of resins may beused alone or in the form of a blend of two or more types.

There is no particular limit to the thickness of the hard-coat layer. Ingeneral, from the viewpoints of prevention of peeling that may be causedduring production and cracking entailed by peeling, the hard-coat layerhas a thickness, for example, suitably in a range of 0.1 to 50 μm,preferably in a range of 0.5 to 8 μm, and more preferably in a range of2 to 5 μm.

The gas barrier layer is categorized into, for example, an organic gasbarrier layer and an inorganic gas barrier layer. There is no particularlimit to a material for forming the organic gas barrier layer. Forexample, materials with low oxygen-permeability including polyvinylalcohol and a partially saponified product thereof, vinyl alcoholpolymers such as ethylene vinyl alcohol copolymer and the like,polyacrylonitrile, polyvinylidene chloride and the like can be used.Among these materials, vinyl alcohol polymers are used most preferablyfrom the viewpoint of their high gas barrier properties.

From the viewpoints of, for example, functionality in terms oftransparency, prevention of coloration, gas barrier properties and thelike, a reduction in thickness, flexibility of a resulting resin sheetand the like, the thickness of the organic gas barrier layer is,preferably not more than 10 μm, more preferably in a range of 2 to 10μm, and most preferably in a range of 3 to 5 μm. With the thicknessbeing not more than 10 μm, in the resin sheet, a lower yellow colorindex (YI value) can be maintained, and with the thickness being notless than 2 μm, a sufficient gas barrier function can be maintained.

Meanwhile, as a material for forming the inorganic gas barrier layer,for example, transparent materials such as silicon oxides, magnesiumoxides, aluminum oxides, zinc oxides and the like can be used. Amongthese materials, silicon oxides and silicon nitrides are used preferablyfrom the viewpoints of, for example, their excellent gas barrierproperties, adhesion to a base material layer and the like.

Preferably, the silicon oxides have, for example, a ratio of the numberof oxygen atoms to the number of silicon atoms of 1.5 to 2.0 for thefollowing reason. That is, with this ratio, the inorganic gas barrierlayer is improved further in terms of, for example, gas barrierproperties, transparency, surface flatness, bending properties, membranestress, cost, and the like. The silicon oxides have a maximum ratio ofthe number of oxygen atoms to the number of silicon atoms of 2.0.

Preferably, the silicon nitrides have, for example, a ratio (Si:N) ofthe number of nitrogen atoms (N) to the number of silicon atoms (Si) of1:1 to 3:4.

There is no particular limit to the thickness of the inorganic gasbarrier layer. Preferably, the inorganic gas barrier layer has athickness in a range of, for example, 5 to 200 nm. With the thicknessbeing not less than 5 nm, for example, more excellent gas barrierproperties can be obtained, and with the thickness being not more than200 nm, the inorganic gas barrier layer is improved also in terms oftransparency, bending properties, membrane stress, and cost.

In the case where the resin sheet according to the present invention isthe laminated body as described above, the thickness of the resin sheetvaries depending on the number of layers in the lamination. In thiscase, the resin sheet has a thickness, for example, preferably in arange of 20 to 800 μm, more preferably in a range of 30 to 500 μm, andmost preferably in a range of 50 to 300 μm. In the case of theabove-mentioned laminated body, the laminated body may include one layercontaining the epoxy resin and the glass fiber cloth-like material ortwo or more such layers.

There is no particular limit to a method of manufacturing theabove-described resin sheet according to the present invention. Theresin sheet can be formed by, for example, the following method. Thatis, the epoxy resin is solidified in the presence of the glass fibercloth-like material. In this case, for example, conventionally knownmethods such as a casting method, a flow-expanding method, animpregnating method, a coating method and the like can be employed.Specifically, the manufacturing of the resin sheet can be performed asfollows.

In the case of the casting method, for example, a glass fiber cloth-likematerial is placed on a flat plate mold, and a liquid epoxy resin iscoated on the cloth-like material. Then, by setting a condition of areduced pressure, the cloth-like material is impregnated with the epoxyresin. After that, for example, by a heating treatment or UVirradiation, the epoxy resin is cured, and thus an epoxy resin layercontaining the glass fiber cloth-like material can be formed.

Furthermore, even under the condition of an atmospheric pressure, anepoxy resin layer containing the glass fiber cloth-like material alsocan be formed by the following method. That is, the glass fibercloth-like material is dipped into a liquid epoxy resin by theimpregnating method, and the epoxy resin is cured in that state.Further, alternatively, the epoxy resin layer may be formed by a methodin which the glass fiber cloth-like material is placed on an endlessbelt or a substrate, and the epoxy resin is impregnated thereinto orcoated thereon.

Furthermore, as required, the coated epoxy resin may be cured by, forexample, a heating treatment, a light irradiating treatment or the like.There is no particular limit to a condition for curing an epoxy resincontaining the dicyclopentadiene type epoxy resin. Preferably, forexample, the curing is performed at a temperature of 100 to 200° C. forten minutes to five hours.

The epoxy resin may be used, for example, in the form of an epoxy resinsolution prepared by dispersing or dissolving the epoxy resin in asolvent. There is no particular limit to the solvent. For example,methyl ethyl ketone, acetone, methyl isobutyl ketone, toluene, xylene,ethyl acetate and the like can be used. The above-mentioned resins ofthe other types and various additives can be added appropriately to aliquid epoxy resin and an epoxy resin solution in which the epoxy resinis dissolved in a solvent.

Furthermore, in the case where the resin sheet according to the presentinvention is a laminated body including a hard-coat layer and the like,the resin sheet should be formed by, for example, the following method.That is, after a hard-coat layer is formed on the flat plate mold, theglass fiber cloth-like material is placed on the hard-coat layer, and anepoxy resin layer is formed in the same manner as described above. Informing the hard-coat layer, as required, curing may be performed by aheating treatment, a light irradiating treatment or the like. Further,in another possible method, a hard-coat layer is formed on an endlessbelt or a base material that is formed from stainless steel or the likeby the flow-expanding method, the coating method or the like, and thenan epoxy resin layer containing the glass fiber cloth-like material isbonded to the hard-coat layer.

There is no particular limit to a method of forming the hard-coat layer.The hard-coat layer should be formed by a method in which a coatingsolution is prepared by mixing the above-mentioned materials into thesolvent, coated on a base material and dried. There is no particularlimit to the coating method, and for example, conventionally knownmethods such as a roll coating method, a spin coating method, a wire barcoating method, a dip coating method, an extrusion method, a curtaincoating method, a spray coating method and the like can be employed.

Furthermore, in the case of a resin sheet including a gas barrier layer,the resin sheet should be formed by, for example, the following method.That is, a gas barrier layer is formed on a hard-coat layer formed asdescribed above, and then an epoxy resin layer containing a glass fibercloth-like material is formed in the same manner as described above.There is no particular limit to a method of forming the gas barrierlayer, and for example, conventionally known methods can be employedappropriately.

The resin sheet according to the present invention can be used forvarious applications. Advantageously, the resin sheet also can be usedas a liquid crystal cell substrate, a substrate for an EL display, and asubstrate for a solar cell, for example. In the case of using the resinsheet as any of various types of substrates as described above, forexample, the resin sheet may be used in the same manner as in the caseof using a conventionally used transparent substrate such as a glasssubstrate or the like.

Furthermore, the resin sheet according to the present invention can beused as a liquid crystal cell substrate in a liquid crystal cell or aliquid crystal display, as a substrate for an EL display in an ELdisplay, and as a substrate for a solar cell in a solar cell or thelike. The various types of substrates can be used as, for example,substitutes for glass substrates and the like used in various types ofconventional displays and solar cells. Through the use of the varioustypes of substrates according to the present invention, for example,sufficient strength can be maintained, and a thickness and weightreduction can be realized. There is no limit to the above-mentionedliquid crystal cells, various types of image displays, solar cells andthe like except that the resin sheet according to the present inventionis used as a substrate. Constituent members other than the substrate andtheir structures can be the same as in the conventional case.

Generally, a liquid crystal display includes a liquid crystal cell inwhich a liquid crystal is held by a liquid crystal cell substrate havingan electrode, a polarizing plate, a reflector, and a backlight, and adriving circuit and the like are incorporated therein. In the liquidcrystal display according to the present invention, the resin sheetaccording to the present invention may be used as a liquid crystal cellsubstrate. Except for this, there is no particular limit to the liquidcrystal display, and the liquid crystal display further may includevarious types of conventionally known constituent components. Thus, inthe liquid crystal display according to the present invention, theliquid crystal cell substrate according to the present invention furthermay be combined with, for example, optical components or the like suchas a light diffusion plate to be provided on a polarizing plate on avisible side, an anti-glare layer, a reflection preventing film, aprotective layer, a protective plate, or a retardation plate forcompensation that is to be provided between a liquid crystal cell and apolarizing plate on the visible side or the like.

Generally, an electroluminescent display is configured with atransparent substrate (substrate for EL display) on which a transparentelectrode, an organic ruminant layer containing a luminant (organicelectroluminescent ruminant), and a metal electrode are laminated inthis order. In an EL display according to the present invention, theresin sheet according to the present invention should be used as asubstrate for EL display. Except for this, there is no particular limitto the EL display, and the EL display further may include various typesof conventionally known constituent components.

The organic luminant layer is a laminated body formed of organic thinfilms containing various types of ruminants. Examples of such alaminated body include: a laminated body of a hole injection layercontaining a triphenylamine derivative or the like and a ruminant layermade of a phosphorous organic solid such as anthracene or the like; alaminated body of the above-mentioned luminant layer and an electroninjection layer containing a perylene derivative or the like; and alaminated body of the above-mentioned hole injection layer, luminantlayer, and electron injection layer, and various such combinations areknown.

In general, an organic electroluminescent display emits light on theprinciple that a voltage is applied to each of the transparent electrodeand the metal electrode so as to inject holes and electrons into theorganic luminant layer, energy generated by re-bonding of these holesand electrons excites the liminant such as a phosphor or the like, andthe excited phosphor radiates the light when it returns to the basisstate. The mechanism of the re-bonding that occurs in the course of thisprocess is the same as in the case of an ordinary diode. As also can beanticipated by this, current and light emitting intensity exhibitconsiderable nonlinearity accompanied with rectification with respect tothe applied voltage.

It is necessary for an organic electroluminescent device that at leastone of the electrodes be transparent so as to obtain luminescence at theorganic luminant layer. In general, a transparent electrode formed of atransparent conductive material such as indium tin oxide (ITO) is usedfor an anode. Meanwhile, the use of substances having small workfunction for a cathode is important in order to facilitate electroninjection thereby to raise luminous efficiency, and in general, metalelectrodes such as Mg—Ag, Al—Li, and the like are used.

In an organic electroluminescent device configured as described above,it is preferable that the organic luminant layer is made of a film thatis as extremely thin as about 10 nm. With this small thickness, forexample, the organic luminant layer can transmit substantially wholelight as the transparent electrode does. As a result, when no light isemitted, light that has entered from the surface of the transparentsubstrate, passed through the transparent electrode and the organicluminant layer, and then been reflected at the metal electrode comes outagain to the surface side of the transparent substrate. Because of this,the display surface of the organic electroluminescent display looks likea mirror when viewed from the exterior.

In the case where the EL device according to the present invention is,for example, an organic EL device that includes a transparent electrodeon the surface side of an organic luminant layer that emits light by theapplication of a voltage, and a metal electrode on the backside of theorganic luminant layer, it is preferable that a polarizing plate isprovided on the surface side of the transparent electrode, and aretardation plate is provided between the transparent electrode and thepolarizing plate.

The retardation plate and the polarizing plate have a function ofpolarizing light that has entered from the exterior and then beenreflected by the metal electrode, thereby providing an effect that themirror of the metal electrode cannot be viewed from the exterior by thepolarizing function. Particularly, the mirror of the metal electrode canbe blocked completely by using a quarter wavelength plate as theretardation plate and adjusting an angle formed by the polarizationdirection of the polarizing plate and the retardation plate to be π/4.That is, of external light entering the organic EL device, only alinearly polarized component can be transmitted by the polarizing plate.Generally, the linearly polarized component of the light is turned intoelliptically polarized light by the retardation plate. Particularly,when the retardation plate is a quarter wavelength plate and when theangle of the polarization direction provided by the polarizing plate andthe retardation plate is π/4, the linearly polarized component is turnedinto circularly polarized light. The circularly polarized light passesthrough the transparent substrate, the transparent electrode, and theorganic thin films. After being reflected by the metal electrode, thelight passes again through the organic thin films, the transparentelectrode, and the transparent substrate, and is turned again intolinearly polarized light by the retardation plate. Since the linearlypolarized light crosses the polarization direction of the polarizingplate at a right angle, it cannot pass through the polarizing plate. Asa result, the mirror of the metal electrode can be blocked completely.

EXAMPLES

Hereinafter, the present invention will be described by way of exampleswith no intention to limit the invention thereto.

Example 1

An epoxy resin mixture was prepared using as an epoxy resin3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate expressed bythe above-mentioned formula (2) (27 parts by weight) and a bisphenol Atype epoxy resin (AER250, trade name (epoxy equivalent of 190);manufactured by Asahi Kasei Corporation) expressed by theabove-mentioned formula (1) (73 parts by weight), as a curing agentmethylhexahydrophthalic anhydride expressed by the following formula (6)(88 parts by weight), and as a curing acceleratortetra-n-butylphosphonium o,o-diethylphosphorodithioate expressed by thefollowing formula (7) (0.9 parts by weight). The preparation wasperformed by mixing the above-mentioned materials under stirring. Then,a glass cloth (Glass Cloth, trade name; manufactured by Nitto BosekiCo., Ltd.) having a refractive index of 1.524 and a thickness of 100 μmwas dipped in the mixture and left to stand for 10 minutes under acondition of a reduced pressure (200 Pa) so that the mixture wasimpregnated into the glass cloth. Thus, a precursor layer in which theglass cloth was embedded was formed.

Meanwhile, a 17 wt % urethane acrylate solution was prepared bydissolving urethane acrylate expressed by the following formula (8) intoluene. Then, the urethane acrylate solution was coated byflow-expanding on a glass plate, and a resulting coating film was winddried so that the toluene solvent was evaporated. The coating film wasthen cured by a UV curing device. As a curing condition, a high-pressuremercury lamp was used, and curing was performed at 200 mJ/cm² for oneminute. Thus, a hard-coat layer having a thickness of 2 μm was formed onthe glass plate.

Subsequently, the precursor layer in which the glass cloth was embeddedwas laminated on the hard-coat layer on the glass plate, and a glassplate that has been subjected to a mold-releasing treatment further waslaminated on the precursor layer. Then, a resulting laminated body wassubjected to a heat treatment so that the precursor layer was cured. Thecuring was performed by one-hour heating at 120° C. further followed byone-hour heating at 150° C. By the curing, an epoxy resin layercontaining the glass cloth was formed on the hard-coat layer. A curedbody containing the epoxy resin has a refractive index of 1.530, andthus a difference in refractive index between the glass cloth and thecured body was 0.006. The refractive index of a portion of the resinlayer (cured body) that contains the epoxy resin except for the glasscloth was determined separately from the manufacturing of the resinsheet. That is, in the same manner as described above except that theglass cloth is not used, the epoxy resin mixture was cured, and therefractive index of a resulting cured body was measured and used as theabove-mentioned refractive index (hereinafter, the same applies).

Then, the glass plates on both surfaces are peeled off, and thus alaminated body of the hard-coat layer and the epoxy resin layer wasobtained. The laminated body was placed on a stainless steel plate andsubjected to after-cure in which the laminated body was left to standfor an hour in an atmosphere of 180° C. and an oxygen concentration of0.5% that was obtained by nitrogen substitution. Thus, a resin sheetthat was the laminated body of the hard-coat layer and the epoxy resinlayer having the glass cloth was obtained. The resin sheet had athickness of 110 μm.

Example 2

An epoxy resin mixture was prepared using3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate expressed bythe above-mentioned formula (2) (78 parts by weight) and an epoxy resinexpressed by the above-mentioned formula (5) in which n=0.2, as a curingagent methyl nadic acid (110 parts by weight), and as a curingaccelerator tetra-n-butylphosphonium o,o-diethylphosphorodithioateexpressed by the above-mentioned formula (7) (2.0 parts by weight). Thepreparation was performed by mixing the above-mentioned materials understirring. Then, in the same manner as in Example 1 except that thismixture and a glass cloth (Glass Cloth, trade name; manufactured byNitto Boseki Co., Ltd.) having a refractive index of 1.513 and athickness of 100 μm were used, a resin sheet that was a laminated bodyof a hard-coat layer and an epoxy resin layer having the glass cloth wasmanufactured. The resin sheet had a thickness of 110 μm, and a curedbody containing the epoxy resin has a refractive index of 1.514, andthus a difference in diffractive index between the glass cloth and thecured body was 0.001.

Comparative Example 1

This comparative example relates to an example of a resin sheet withouta glass cloth. An epoxy resin solution that was the same as that used inExample 1 was coated by flow-expanding on a hard-coat layer that was thesame as that used in Example 1 so that a precursor layer was formedthereon. The precursor layer was subjected to a heating treatment so asto be cured. The same curing condition as that used in Example 1 wasused. By the curing, an epoxy resin layer having a thickness of 100 μmwas formed on the hard-coat layer. Next, a laminated body of thehard-coat layer and the epoxy resin layer was peeled off of the endlessbelt and then subjected to after-cure under the same condition as thatused in Example 1.

Comparative Example 2

This comparative example relates to an example in which glass beads areused in place of a glass cloth. In the same manner as in ComparativeExample 1 except that an epoxy resin solution containing a filler wasprepared by mixing 70 parts by weight of spherical glass beads having amean particle diameter of 120 μm (refractive index: 1.524) into an epoxyresin solution that was the same as that used in Example 1, a resinsheet that was a laminated body of a hard-coat layer and an epoxy resinlayer was manufactured.

Comparative Example 3

A resin sheet was manufactured in the same manner as in Example 2 exceptthat a glass cloth (Glass Cloth, trade name; manufactured by NittoBoseki Co., Ltd.) having a refractive index of 1.558 and a thickness of100 μm was used as a glass cloth. A cured body containing an epoxy resinhas a refractive index of 1.514, and thus a difference in refractiveindex between the glass cloth and the cured body was 0.044.

With respect to each of the resin sheets obtained as described above,the following evaluation tests were performed. The results thereof areshown in Table 1 below.

1. Coefficient of Linear Expansion

Using a TMA/SS150C, trade name (manufactured by Seiko Instruments Inc.),TMA values (μm) at temperatures of 25° C. and 160° C. were measured, anddetermination was performed in the above-mentioned manner.

2. Bending Property Test

Each of the resin sheets was wound around a steel mast having a diameterof 35 mm, and a visual observation was performed to check if a crack hadbeen caused.

3. Light Transmittance (%)

With respect to each of the resin sheets, a total transmittance of lightrays of λ=550 nm was measured using a high-speed spectrophotometer(DOT-3C, trade name; manufactured by Murakami Color ResearchLaboratory).

4. In-plane Retardation (Δnd) and Retardation in Thickness Direction(Rth)

With respect to each of the resin sheets, an in-plane retardation and aretardation in a thickness direction were determined based on arefractive index at 590 nm using KOBRA21ADH, trade name of OjiScientific Instruments.

5. Surface Roughness

With respect to each of the resin sheets, a surface roughness(difference between a maximum value and a minimum value) was measuredusing a stylus type surface roughness meter (for example, P-11, tradename; manufactured by KLA-Tencor Japan Ltd.) under a condition of a longwavelength cut-off of 800 μm, a short wavelength cut-off of 250 μm, andan evaluation length of 10 mm. The measurement of the surface roughnesswas performed with respect to each of a surface on the epoxy resin layerside and a surface on the hard-coat layer side. In Table 1 below, thesurface roughness of the surface on the epoxy resin layer side wasindicated as “Rt(E)”, and the surface roughness of the surface on thehard-coat layer side was indicated as “Rt(H)”.

6. Haze Value

With respect to each of the resin sheets, a haze value was measuredusing a hazemeter (HM-150, trade name; manufactured by Murakami ColorResearch Laboratory).

TABLE 1 Coefficient of linear Light trans- Haze Rt Rt expansion mittanceBending Δnd Rth value (E) (H) (/° C.) (%) properties (nm) (nm) (%) (μm)(μm) Ex. 1 1.8 × 10⁻⁵ 90 No crack 1.5 42 8 0.7 0.7 caused Ex. 2 1.5 ×10⁻⁵ 90 No crack 0.2 9 2.5 0.6 0.6 caused Com. 6.5 × 10⁻⁵ 92 No crack0.2 40 0 0.02 0.02 Ex. 1 caused Com. 2.6 × 10⁻⁵ 89 Crack 0.2 40 10 0.40.4 Ex. 2 caused Com. 1.5 × 10⁻⁵ 89 No crack N.D N.D 83 0.6 0.6 Ex. 3caused N.D: Not determinable

As shown in Table 1, in the resin sheet of Comparative Example 2, sincethe glass beads were contained therein, while a low coefficient oflinear expansion could be obtained, bending properties weredeteriorated, resulting in the occurrence of a crack. Meanwhile, inComparative Example 1 without a glass cloth, while no crack was caused,an extremely high coefficient of linear expansion was obtained. Incontrast to this, in the resin sheet of Example 1, a low coefficient oflinear expansion was obtained, and moreover, excellent bendingproperties and light transmittance also were attained. Further, in theresin sheet of Comparative Example 3, since the difference in refractiveindex between the glass cloth and the epoxy resin cured body was large,the resin sheet exhibited an extremely high haze value and thus couldnot be used as a transmission-type liquid crystal cell substrate. Asexplained by the foregoing description, according to the presentinvention, a resin sheet with a low coefficient of linear expansion canbe obtained, in which cracking is not likely to occur even on impactduring transport and an excellent transparency also is attained.Moreover, as shown in Example 2, through the use of an epoxy resinhaving the dicyclopentadiene skeleton expressed by the above-mentionedformula (5), the resin sheet that exhibited an even smaller value of Rthcould be obtained.

INDUSTRIAL APPLICABILITY

As described in the foregoing discussion, the resin sheet according tothe present invention includes a glass fiber cloth-like material and anepoxy resin and thus, for example, suppresses thermal expansion or thelike and exhibits excellent strength. Thus, patterning deviation causeddue to thermal expansion is suppressed, and moreover, rupture is notcaused even on impact during transport or assembly of various types ofdisplays such as a liquid crystal and the like, thereby also providingexcellent production efficiency. In addition, the resin sheet accordingto the present invention has a haze value of 10% or lower. Therefore,the resin sheet has excellent transparency, and thus is useful for, forexample, a transmission-type liquid crystal cell substrate. Thus, whenthe resin sheet according to the present invention is used as any of thevarious types of substrates described above, various types of displaysand a solar cell that not only achieve weight and thickness reductionbut also exhibit excellent strength and transparency can be obtained.

1. A resin sheet, comprising an epoxy resin and a glass fiber cloth-likematerial, wherein the resin sheet comprises the glass fiber cloth-likematerial and a resin layer containing the epoxy resin, such that anabsolute value of a difference between a refractive index of the glassfiber cloth-like material and a refractive index of the resin layer is 0to 0.01, and wherein the resin sheet has a haze value of 10% or lower,an in-plane retardation of not more than 2 nm, and a retardation in athickness direction of not more than 40 nm.
 2. The resin sheet accordingto claim 1, wherein the resin sheet has a coefficient of linearexpansion of not more than 3.00×10⁻⁵/° C. at a temperature of 25° C. to160° C.
 3. The resin sheet according to claim 1, wherein the resin sheethas a light transmittance of 88% or higher.
 4. The resin sheet accordingto claim 1, wherein the resin sheet has a surface roughness (Rt) of notmore than 2 μm.
 5. The resin sheet according to claim 1, wherein theglass fiber cloth-like material is included in the resin sheet at aratio in a range of 20 to 80 wt %.
 6. The resin sheet according to claim1, wherein the resin sheet is a single-layered body into which the glassfiber cloth-like material and the resin layer containing the epoxy resinare integrated.
 7. The resin sheet according to claim 1, wherein theresin layer is formed of the epoxy resin that is cured in a state ofbeing impregnated into the glass fiber cloth-like material.
 8. The resinsheet according to claim 1, wherein the glass fiber cloth-like materialis embedded in the resin layer containing the epoxy resin.
 9. The resinsheet according to claim 1, further comprising a hard-coat layer. 10.The resin sheet according to claim 1, further comprising a gas barrierlayer.
 11. A liquid crystal cell substrate comprising a resin sheet asclaimed in claim
 1. 12. A liquid crystal cell comprising a liquidcrystal cell substrate as claimed in claim 11 and a liquid crystal. 13.A liquid crystal display comprising a liquid crystal cell as claimed inclaim
 12. 14. An image display comprising a resin sheet as claimed inclaim
 1. 15. A substrate for electroluminescent display comprising aresin sheet as claimed in claim
 1. 16. An electroluminescent displaycomprising a substrate for electroluminescent display as claimed inclaim
 15. 17. A substrate for a solar cell comprising a resin sheet asclaimed in claim
 1. 18. A solar cell comprising a substrate for a solarcell as claimed in claim 17.